Figure 1. Morphology of Phytophthora botryosa. Sporangia are caducous with medium-length stalks and are produced in a sympodium. Oogonia are globose, and antheridia are paragynous. (Courtesy A. Vaziri; Reproduced from Erwin and Ribeiro, 1996)

 

Figure 2. Culture of Phytophthora botryosa grown on V-8 juice agar. (Courtesy Jean B. Ristaino)

 

Figure 3. Sporangia of Phytophthora botryosa form in sympodium in clumps (×1,000). (Courtesy Jean B. Ristaino)

 

Figure 4. Oogonium of Phytophthora botryosa with a spherical amphigynous antheridium (×1,000). Produce by a cross with Phytophthora capsici. (Courtesy Jean B. Ristaino)

 

Introduction

Phytophthora botryosa  Chee (1969)

 

Phytophthora botryosa was first isolated from leaf petioles of the rubber tree (Hevea brasiliensis) in Malaysia and Thailand and described by Chee in 1969. The pathogen causes leaf fall and pod rot of rubber trees (Chee, 1969; Chee and Wastie, 1980) and pod rot of cacao (Chee and Wastie, 1970) and has been reported on taro (Zheng and Lu, 1989). It is classified in group II by Stamps (1985) and Stamps et al. (1990) (Fig. 1).

Cultural Characteristics

Colonies are slow growing and slightly radiate with little aerial mycelium (Fig. 2). The minimum temperature for growth is 9°C, the optimum temperature for growth is 26°C, and the maximum temperature for growth is 32°C. There is no colony growth at 35°C or higher.

Reproductive Structures

Asexual Structures

 

Sporangiophores:

Sporangiophores are sympodial.

 

Sporangia:

Sporangia are papillate and spherical, ovoid, ellipsoidal, or obturbinate and are 20–51 × 28–69 µm (Fig. 3). Sporangia are caducous with a medium pedicel length of 10–20 µm or less. Length–breadth ratios are 1.6–2.1. Sporangia form in botryose clumps.

 

Chlamydospores:

Chlamydospores are produced infrequently (sparse) and are 14–30 µm (average 18.7 µm).

 

Sexual Structures

 

P. botryosa is heterothallic and produces oospores when paired with differing mating types (A1 and A2). There are occasional oospores in single culture.

 

Antheridia:

Antheridia are amphigynous, spherical, and 8–12 × 12.5–21 µm.

 

Oogonia:

Oogonia are smooth walled, hyaline to yellow, and 21.7–31.7 µm (average 28 µm).

 

Oospores:

Oospores form abundantly in host tissues and have a diameter of 20.9–27.6 µm (average 25.1 µm) (Fig. 4).

Host Range and Distribution

Host

Common Name

Disease

Geographical Distribution

Hevea brasiliensis

Rubber tree

Green pod decay

Malaysia, Thailand, Vietnam, Andaman Islands

Colocasia esculenta

Taro

Root rot

China

Theobroma cacao

Cocoa

Pod rot

Malaysia

Symptoms

Symptoms are similar to those of P. meadii on Hevea spp. The pathogen attacks the fruit, leaves, bark, and green shoots of the rubber tree. The symptoms on the fruit include dullish gray spots that develop at the stem end and spread across the entire fruit. It causes leaf fall and branch dieback. The pathogen can survive in bark cankers and causes a "stripe canker" on the bark (Erwin and Ribeiro, 1996).

References

Chee, K. H. 1969. Variability of Phytophthora species from Hevea brasiliensis. Trans. Br. Mycol. Soc. 52:425-436.

 

Chee, K. H., and Wastie, R. L. 1970. Black pod disease of cacao. Planter, Kuala Lumpur. 46:294-297.

 

Chee, K. H., and Wastie, R. L. 1980. The status and future prospects of rubber diseases in tropical America. Rev. Plant Pathol. 59:541-548.

 

Erwin, D. C., and Ribeiro, O. K. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.

 

Stamps, D. J. 1985. Phytophthora botryosa. CMI Descr. Pathog. Fungi Bact. 835:1-2.

 

Stamps, D. J., Newhook, F. J., Waterhouse, G. M., and Hall, G. S. 1990. Revised tabular key to the species of Phytophthora de Bary. Mycol. Pap. 162. CAB International, Wallingford, United Kingdom; Commonwealth Mycological Institute, Kew, Surrey, England.

 

Zheng, X. B., and Lu, J. Y. 1989. Studies on the Phytophthora species in Fujian, Zhejiang, Jiangsu provinces and Shanghai, China. Acta Mycol. Sin. 8:161-168.